A mobile phone or other bearer device may be secured using a security token such as a smart card to authenticate an owner of the smart card. Before the smart card is activated to authenticate the owner, the smart card may require the owner to communicate a secret such as a personal identification number (PIN) shared between the smart card and the owner. To avoid burdening the owner, the smart card may require the owner only to provide the PIN at certain extended intervals. In many cases, the smart card may remain activated for hours, weeks, or even months. If the bearer device is stolen while the smart card is activated, the thief may use the stolen bearer device to access or charge secure services using the activated smart card to authenticate himself as the owner.